EL 1319 Nicholson River, Annual report for year ending 7-8-1979.

Abstract

At the end of the reporting period the Hunting Photogeological map of the western part of the project area was not complete. Verbal progress reporting however, has indicated a base metal potential within the area in addition to the uranium potential. The latter is based on the 'look alike' regional geology to the Alligator Rivers area. In particular the similarities lie in the nature of and the relationship between Murphy Metamorphics, Nicholson Granite. Complex and the unconformably overlying Carpentarian sandstones. The base metal potential, lies in the Fickling Group sediments which are considered to be the stratigraphic equivalent of the McArthur Group, hosts to the McArthur River (HYC) Pb-Zn deposits. Within EL 1319 a fault bounded confined basin of sickling Group pyritic and dolomitic siltstones and shales with interbeddeu dolomites has been recognised. A total of 94 uranium (Bi 214) channel anomalies were defined with the project area. Initial ground checking of these anomalies was completed at the end of July 1979. Weak anomalies that were not verified by the airborne rechecking phase were not ground checked unless they fell in very favorable geological situations. Analog records of each anomaly are included in the hardcopy of the company report and anomaly locations are also shown. Anomalies can be grouped under the follow headings: 1. Murphy Metamorphic hosted; A total of 5 anomalies have been located in the Lower Proterozoic Murphy Metamorphics and of these only one (31702) occurs at or near the Carpentarian or Adelaidean unconformity. 31702 is a very low order anomaly reflecting a sharp background change between the Fish River Formation sandstones (llOcps) and the quartzofeldspathic schists and pegmatites of the Murphy Metamorphics which outcrop at the break of slope below the sandstone escarpment. 3901 and 4101 occur in the area of 'Anomaly 30' as described and investigated by United Uranium NL. and Noranda. 4702 lies about 1500m along strike. These anomalies are in ferruginized and silicified siltstones adjacent to major ENE trending fault zone. In 1972 Noranda drilled 7 vertical percussion holes to a maximum depth of 60m in the area of anomaly 3901. These of these holes intersected anomalous uranium values up to 115 ppm U308 over intersection widths of up to 8m in hematitic sandy siltstone. Anoma1y 4901 is the most promising anomaly in the Murphy Metamorphics. The peak of the anomaly occurs in a fault breccia in micaceous siltstones and quartz biotite schists. Readings of up to 1500 cps have been noted on the breccia. Outcrop in the area is poor and the breccia can only be traced for 20-30 metres along strike. 2. Nicholson Granite hosted; A number of anomalies were found to be in the early Carpentariarn Nicholson Granite. This is a multi-intrusion, multi-phase granite with widely varying radiometric backgrounds. Many of these anomalies were found to be due to high background phases. Other anomalies are due to small outcrop areas of high background granite exposed between lower background cover such as overlying Carpentarian sandstones or Recent alluvium. All these have been downgraded. 3. Hot springs and black soils; 20 Individual 'hot' spring anomalies were located. 15 of these are over the previously known Dingo Creek springs (U.U.N.L. 1971) and 3 more occur in an unnamed drainage 4km east of Dingo Creek. These springs all drain from a major E-W joint set at the Constance Sandstone/Wallis Siltstone Member contact. Anomaly 26101 is an identical anomaly in the same geological situation about 8km west cf Dingo Creek. Anomaly 34401 is a similar 'hot' spring anomaly draining the Carpentarian unconformity between Fish River Formation and ? Nicholson Granite. Anomaly 18402 is a dried black soil swamp probably overlying Nicholson granite. The black soil has a high background (200 cps/lOO cps) and is probably due to scavenging of uranium from surface water. 4. High background units in Carpentarian & Adelaidean sediments; 4. A number of anomalies were found over high background units within the Carpentarian or Adelaidean sedimentary-volcanic sequences. Many of these are in fact volcanic units with high radiometric background compared with the adjacent quartzites and sandstones. A few anomalies are due to ferruginous slump breccias in the Fish River Formation. At the 42401 system (5 individual anomalies) one such slump breccia has been involved in later vertical fracturing and more intense ferruginization. Anomalies up to 1500 cps on 50 cps background have been located along this structure in the breccias. The anomaly is 500-600 metres horizontally from the Carpentarian unconformity and approximately 300-400 metres vertically above it. 5. Laterites; 5. Iron rich laterites have been developed on some sandstone units in the Carperitarian and Adelaidean sequences. Some of these have accumulated significantly anomalous uranium values at surface. One of these anomalies was investigated and drilled by Noranda In 1973. These anomalies have been downgraded. CONCLUSIONS & RECOMMENDATIONS; 1. A large number of previously unknown anomalies were located by the airborne radiometric survey. A considerable proportion of these are due to surface accumulations in laterites and black soils or to sharp background changes at geological boundaries. These anomalies have been downgraded and do not justify further follow up, 2. Five anomalies occur in the Murphy Metamorphics (3901, 4101, 4702, 4901 and 31702). Although the surface anomalies are generally weak (except 4901) it is recommended that detailed follow up be carried out on all of these anomalies because of their favorable geological situations.